1. Field of the Invention
The subject matter disclosed herein relates to metal getter systems for use in electronic devices. Particularly, the getter systems taught herein are useful in the electrolytic environment within electrolytic devices and, more particularly, include composite getter systems that can be used in electrolytic capacitors without passivation.
2. Description of the Related Art
Electronic devices are used extensively in many applications, and getters are used in the manufacture and operation of these important devices in countless industrial and consumer applications. A getter is typically composed of metal or a metal alloy that exhibits a chemical affinity for specific gases and, when introduced into an evacuated device, absorbs the targeted gaseous molecules that are present to create and maintain an appropriate vacuum in the device. Notably, there has been a long-felt need for a gaseous contaminant getter or sorber for liquid environments in which the getter is both efficient and resistant to passivation. Such liquid environments, for example, include those environments present in electrolytic devices, such as the electrolytic liquid environments of electrolytic capacitors.
Electrolytic devices include those devices in which the conduction of electricity is accompanied by a chemical action. The electrolytic capacitor is an example of an electrolytic device. The electrochemical double layer capacitor (EDLC), for example, is a supercapacitor and typically includes an airtight housing that encloses electrodes, typically formed of metal sheets, which are immersed in, or impregnated with, an electrolytic solution. The metal sheets are electrically coupled to the outside of the housing by a pair of electrical contacts. The problem is that capacitors can also contain contaminants that can damage the capacitor, sometimes beyond repair, unless the capacitor has some sort of contaminant removal mechanism. These contaminants can be gases, for example, and can be created during operation of the capacitor or by the desorption of such gases from various parts of the capacitor. One type of harmful gas is hydrogen.
The problem is that metal getters become passivated in liquid environments, such as the electrolytic environments of electrolytic capacitors. The term “passivation,” as used herein, refers to a metal getter being rendered at least generally incapable of sorbing contaminants, such that the getter material is undesirable for its intended purpose. One attempted solution to the problem of passivation has been to create a “non-mixed” sorbing system, wherein the getters are not mixed with the electrolytic solution. Another attempted solution to the problem has been to create a “mixed sorbing system” by mixing select getters, such as liquid getters, with the electrolytic solution. An example of such as system is disclosed in International Patent Application PCT/IT2006/000343 in the name of SAES Getters SpA, hereby incorporated herein in its entirety by reference. An example of a mixed sorbing system using solid sorbers is described in JP 03-292712, hereby incorporated herein in its entirety by reference, wherein an additive including a particulate of platinum, palladium, or alloys thereof, is applied onto electrolytic solution-impregnated paper sheets. Unfortunately, the paper sheets are quite thin, often less than 10 μm in thickness, and may be easily damaged by the added particles and result in short-circuits within the capacitor.
Another attempted solution to the problem has included the use of polymeric barriers to shield the getter materials from the electrolyte. These barriers have allowed for the use of very effective getter materials in electrolyte environments, where the getter material would otherwise be subject to passivation. An example of such a system is disclosed in Italian App. Nos. MI2005A002344, by SAES Getters SpA, and MI2006A000056, by SAES Getters SpA, each of which is hereby incorporated herein in its entirety by reference. Unfortunately, such polymer barriers, although permeable to the contaminant to allow for sorption, are also designed to be impermeable to the electrolyte in order to protect the getter material from passivation, resulting in inefficiencies. Moreover, such polymeric systems tend to be expensive and difficult to use.
Accordingly, one of skill will appreciate a solid, composite getter system that is easy to use in an electrolyte environment and can be used to address passivation. Solid, composite getters have been used so far only in evacuated or gaseous environments, as they were never expected to be workable in liquid-containing environments known to passivate the getter materials.